Ellipse drawing compass

ABSTRACT

A compass for drawing ellipses has a hand held center post terminating in a lower pin, a first spur gear fixed to the post, a swing arm rotatable about the post, a second spur gear one half the pitch diameter of the first spur gear mounted on the arm and engaging the first spur gear, a first set of miter gears, one being connected to the second spur gear and the other driving a shaft mounted to extend along the arm, a second set of miter gears, one being slidably mounted on the shaft and the other being mounted vertically on a bracket slidable on the arm, a vertical shaft extending from the vertically mounted miter gear on the bracket, and an adjustable beam attached between the vertical shaft and a writing point, the writing point scribing an ellipse as the arm is swung about the post by a handle mounted at the free end of the arm.

United States Patent [1 1 Armitt 1 Dec. 17, 1974 ELLIPSE DRAWING COMPASS [76] Inventor: Roy Jesse Armitt, 314 St. George St., Toronto, Ontario, Canada 22 Filed: Feb. 12, 1 974 21 Appl. No.: 441,755

Primary Examiner-Harry N. Haroian Attorney, Agent, or FirmPeter L. Tailer [5 7 ABSTRACT A compass for drawing ellipses has a hand held center post terminating in a lower pin, a first spur gear fixed to the post, a swing arm rotatable about the post, a second spur gear one half the pitch diameter of the first spur gear mounted on the arm and'engaging the first spur gear, a first set of miter gears, one being connected to the second spur gear and the other driving a shaft mounted to extend along the arm, a second set of miter gears, one being slidably mounted on the shaft and the other being mounted vertically on a bracket slidable on the arm, a vertical shaft extending from the vertically mounted miter gear on the bracket, and an adjustable beam attached between the vertical shaft and a writing point, the writing point scribing an ellipse as the arm is swung about the post by a handle mounted at the free end of the arm.

1 Claim, 4 Drawing Figures 1 1 ELLIPSE DRAWING COMPASS BACKGROUND OF THE INVENTION Ellipse drawing devices are known, but they are complex, difficult to use, and costly to manufacture. The ellipse drawing compass of this invention is inexpensive to manufacture and easy to use.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a side view of the ellipse drawing compass of my invention;

FIG. 2 is a top view of the compass of FIG. 1 with a broken away end of the compass shown swung through DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIGS. 1 and 2, my ellipse drawing compass has a center post with a solid knurled upper handle 11 formed integrally therewith. Post 10 has a spur gear 12 fixed to it and terminates in the lower holder 13 for a center pin 14. The holder 13 and the pin 14 may be similar to those used in conventional drawing instruments.

An arm 15 is pivotally mounted on post 10 above spur gear 12 by a centrally disposed horizontal portion 16. A second spur gear 17 is mounted on a short shaft 18 on arm portion 16 to mesh with gear 12. Shaft 18 extends through portion 16 and has miter gear 19 of a first pair of miter gears 19 and 20 mounted on it. Miter gear 20 is fixed to the end of a longitudinal horizontal shaft 21 which is journalled at each end in the vertically bent portions 22 and 23 of arm 15. A long horizontal portion 24 of arm 15 extends between the vertical portions 22 and 23. Thus it may be seen that arm 15 may be formed by making three bends in a length of flat stock.

Shaft 21 is square in section to slidably mount thereon miter gear 26 of the second pair of miter gears 26 and 27. A bracket 28 has a top flange 29 which is slidably secured on horizontal portion 24 of arm 15. A lock screw 30 fixes bracket 28 in any set position along portion 24. The vertical back 31 of bracket 28 holds miter gear 26 in engagement with miter gear 27 and the horizontal foot 32 of bracket 28 journals the vertical shaft 33 on which miter gear 27 is fixed. The lower end of shaft 33 has a clamp 34 fixed thereto.

Beam 35 is fixed in clamp 34 and has fixed to it the clamp 36 which mounts the drawing instrument holder 37 shown holding a lead 38. Welded or otherwise fixed to project upward from the free end of arm 15 is a shaft 40 with a knurled handle 41 on its upper end. If desired, handle 41 may be rotatably mounted on shaft 40.

This invention is used and functions in the following manner. If an ellipse 42 is to be drawn, indicator line 43 on bracket 28 is set on scale 44 at a given value. This value or reading on scale 44 is the distance from the center pin 14 to the axis of shaft 33. Beam 35 is positioned by setting clamps 36 and 34 so that the axis of shaft 33 and drawing element 38 are a given distance apart. These distances are designated A and B in FIGS. 1 and 3. If it is desired to draw an ellipse with a given major and minor axis, the distance A is one quarter the sum of the major and the minor axis and the distance B is one quarter the difference between the major and the minor axis. This results from the fact that the major axis of an ellipse is 2(A+B) and the minor axis is 2(A-B). Distance be may be set using a ruler to locate the clamps 34 and 36 along beam 35.

Once the instrument is set, post 10 is placed with its point 14 at a center 0, arm 15 is aligned with the minor axis of the ellipse to be drawn, and handle 11 is rotated to align beam 35 with arm 15 as shown in FIGS. 1 and 2. Beam 35 may be directly grasped by the fingers and aligned, if desired. Handle 11 is then held in a vertical position and held from rotating while arm 15 is swung through 360 about post 10 by means of handle 41 to draw an ellipse 42. Beam 35 may be extended away from post 10 and aligned with arm 15 along the major axis of an ellipse if desired. Drawing pens or other drawing devices may be substituted for lead 38.

Beam 35. makes two revolutions relative to arm 15 for each 360 swing of the arm 15. If an ellipse 42 is drawn with a small minor axis compared with its major axis, a long beam 35 as shown in FIG. 4, will project from clamp 34 far enough to strike holder 13 of post 10. Thus for each size of ellipse drawing compass a shorter and a longer beam 35 and 35 should be provided to allow for maximum versatility.

While spur gears 12 and 17 with a two to one ratio used with two sets of miter gears 19 and 20, and 26 and 27 are shown, the gears need only be chosen to rotate shaft 33 twice relative to arm 15 for each complete circle swung by arm 15. While this invention has been shown and described in the best form known, it will nevertheless be understood that this is purely exemplary and that modifications may be made without departing from the spirit of the invention.

What is claimed is:

1. A compass for drawing ellipses comprising, in combination, a center post having a first handle at its upper end and a pin at its lower end; a first spur gear fixed to said center post; an arm of flat stock having a centrally disposed end pivotally mounted on said center post above said first spur gear and a free end having an inner vertical portion bent upward from said centrally disposed end, a horizontal portion bent outward from the top of said inner vertical portion, and an outer vertical portion bent downward from said horizontal portion; a first shaft extending through and being journalled in said centrally disposed end of said arm; a sec ond spur gear mounted on said first shaft below the centrally disposed end of said arm and meshing with said first spur gear, said second spur gear having a pitch diameter one half that of said first spur gear; a longitudinal shaft journalled in said inner and outer vertical portions below said horizontal portion of said arm; a first set of meshing first and second miter gears, said first miter gear being mounted on said longitudinal shaft and said second miter gear being mounted on said first shaft above the centrally disposed end of said arm; a downward extending second vertical shaft; a second set of meshing third and fourth miter gears, said third miter gear being slidably mounted on said longitudinal shaft; a bracket having a top flange slidably disposed about said horizontal portion of said arm, clamping means on said top flange to lock said bracket along said horizontal portion of said arm, a vertical back engaging said third miter gear holding said third miter gear in said beam an adjustable distance from said second vertical shaft; and a second handle at the free end of said arm so that, when said first handle is held and said arm is swung through 360 by said second handle. said gears rotate said second vertical shaft twice relative to said arm and said drawing element scribes an ellipse. 

1. A compass for drawing ellipses comprising, in combination, a center post having a first handle at its upper end and a pin at its lower end; a first spur gear fixed to said center post; an arm of flat stock having a centrally disposed end pivotally mounted on said center post above said first spur gear and a free end having an inner vertical portion bent upward from said centrally disposed end, a horizontal portion bent outward from the top of said inner vertical portion, and an outer vertical portion bent downward from said horizontal portion; a first shaft extending through and being journalled in said centrally disposed end of said arm; a second spur gear mounted on said first shaft below the centrally disposed end of said arm and meshing with said first spur gear, said second spur gear having a pitch diameter one half that of said first spur gear; a longitudinal shaft journalled in said inner and outer vertical portions below said horizontal portion of said arm; a first set of meshing first and second miter gears, said first miter gear being mounted on said longitudinal shaft and said second miter gear being mounted on said first shaft above the centrally disposed end of said arm; a downward extending second vertical shaft; a second set of meshing third and fourth miter gears, said third miter gear being slidably mounted on said longitudinal shaft; a bracket having a top flange slidably disposed about said horizontal portion of said arm, clamping means on said top flange to lock said bracket along said horizontal portion of said arm, a vertical back engaging said third miter gear holdIng said third miter gear in mesh with said fourth miter gear, and a horizontal foot extending from said vertical back under said longitudinal shaft and said top flange, said downward extending second vertical shaft being journalled in said horizontal foot with said fourth miter gear being mounted on said vertical shaft; a drawing element; a beam; a first clamp adjustably fixing said beam to said second vertical shaft; a second clamp fixing said drawing element along said beam an adjustable distance from said second vertical shaft; and a second handle at the free end of said arm so that, when said first handle is held and said arm is swung through 360* by said second handle, said gears rotate said second vertical shaft twice relative to said arm and said drawing element scribes an ellipse. 